December 20, 1912] 



SCIENCE 



873 



in the enclosure, cover them with the cover- 

 glass, place a drop of solution containing par- 

 amecia at the opening in the enclosure, and 

 then study the process of feeding under low 

 or high power at the place where the two solu- 

 tions meet. Didinia thus enclosed can be 

 studied for hours without danger from drying 

 and if put into a damp chamber when not in 

 use they can often be kept for days. This is 

 an excellent method for observation on all 

 sorts of protozoa. 



2. A few seconds after adding paramecia 

 to a solution containing many didinia kill 

 theta suddenly by flooding the dish with a lib- 

 eral supply of Worcester's fluid. If the ani- 

 mals are killed at just the right time speci- 

 mens in all stages of the process of feeding 

 will be found. These can be mounted and 

 studied at leisure under any magniflcation 

 desired. If the animals are treated with 

 glycerine as described above the different 

 structures stand out very distinctly. I used 

 this method in demonstrating the protective 

 function of the trichocysts. In order to do 

 this it is, however, necessary to have relatively 

 large paramecia and small didinia. 



Another very interesting and instructive 

 process that can be observed readily in 

 Didinium is encystment. Although this is a 

 protective process of the greatest importance 

 in many organisms, it is rarely studied flrst 

 hand. Didinia can be induced to encyst al- 

 most any time by cutting off the food supply 

 and adding considerable decaying organic 

 matter, and as previously stated they can be 

 induced to develop and become active again 

 by adding a strong culture of paramecia. 

 Different stages in these processes can fre- 

 quently be seen, as for example the disappear- 

 ance of the cilia, mouth seizing-organ, macro- 

 nucleus, etc. 



Conjugation occurs abundantly at times in 

 Didinium, but the environmental factors 

 necessary to induce it have not as yet been 

 ascertained with sufficient accuracy to make 

 this form at all favorable for the study of this 

 process. Fission, on the other hand, occurs 

 more frequently than in Paramecium and 



many other protozoa and the essential fea- 

 tures in the process are easily worked out. 



It seems to me then that owing to the 

 readiness with which Didinium can be pro- 

 cured at any time, the ease with which its 

 structures can be worked out, and the possi- 

 bility of observing the phenomena of flssion 

 and encystment and especially the marvelous 

 process of feeding, this animal should become 

 as familiar in biological laboratories as Para- 

 mecium now is. In fact, the study of Para- 

 mecium must be regarded as very superficial 

 indeed without observations on Didinium and 

 its method of protection against this deadly 

 enemy. 



LITERATURE 



Balbiani, E. G. 1873. "Observations sur le 

 Didinium nasuUim," Arch. d. Zool. Exp., Vol. 2, 

 pp. 363-394. 



Thou, Karel. 1905. "Ueber den feineren Bau 

 von Didinium nasutum O. F. M.," Protisten- 

 kunde, Vols. 5-6, pp. 280-315. 



Mast, S. O. 1909. "The Eeaetions of Didinimm 

 nasutum (Stein) with Special Eeference to the 

 Feeding Habits and the Function of Tricho- 

 cysts," Biol. Bull., Vol. 16, pp. 91-118. 



S. O. Mast 

 Johns Hopkins University 



the numbers of insects destroyed by western 



MEDDOWLARES (STURNELLA NEGLECTa) 



Little definite data as to the exact numbers 

 of insects destroyed by birds in a given local- 

 ity has as yet been available. In connection 

 with an investigation into the food habits of 

 certain California birds now being carried on 

 by the California State Board of Fish and 

 Game Commissioners, and the University of 

 California, considerable evidence as to the toll 

 of insects taken by certain species of birds is 

 being made available. With the help of the 

 deputies of the commission it has been pos- 

 sible to collect birds in sufiicient quantities 

 for stomach examination, in some twenty dif- 

 ferent parts of the state, and in every month 

 of the year. A knowledge of the food habits 

 of the birds throughout the year is therefore 

 at hand. 



